The present invention relates generally to methods of inhibiting the corrosion of metal surfaces by aqueous acids in oil and gas operations.
Subterranean hydrocarbon containing formations penetrated by well bores are often treated with aqueous acids to stimulate the production of hydrocarbons therefrom. One such treatment, generally referred to as “acidizing” involves the introduction of an aqueous acid solution into a subterranean formation under pressure so that the acid solution flows through the pore spaces of the formation. The acid reacts with acid soluble materials contained in the formation thereby increasing the size of the pore spaces, thus increasing the permeability of the formation. Another production stimulation treatment known as “fracture-acidizing” involves the formation of one or more fractures in the formation and the introduction of an aqueous acid solution into the fractures to etch the fracture faces whereby channels are formed therein when the fractures close. The acid also enlarges the pore spaces in the fracture faces and in the formation.
Acidizing and fracture-acidizing solutions typically contain, for example, 15% to 28% by weight of hydrochloric acid, which can cause corrosion of metal surfaces in pumps, tubular goods and equipment used to introduce the aqueous acid solutions into the subterranean formations to be treated. The expense associated with repairing or replacing corrosion damaged tubular goods and equipment can be problematic. The corrosion of tubular goods and down-hole equipment is increased by the elevated temperatures encountered in deep formations, and the corrosion results in at least the partial neutralization of the acid before it reacts with acid-soluble materials in the formations, which leads to added expense and complications because additional quantities of the acid often are required to achieve the desired result.
Aqueous acid solutions are also utilized in a variety of other industrial applications to contact and react with acid soluble materials. In such applications, metal surfaces are contacted with the acid and any corrosion of the metal surfaces is highly undesirable. In addition, other corrosive fluids such as aqueous alkaline solutions, heavy brines, petroleum streams containing acidic materials and the like corrode metal surfaces in tubular goods, pipelines and pumping equipment during transportation, storage and treatment phases.
A variety of metal corrosion inhibiting additives have been developed for aqueous acid fluids. Typical corrosion inhibitors for use in acidizing operations are based on, for example, propargyl alcohols, long chain hydrophobic tertiary amines, or quaternary ammonium compounds. These compounds, however, are known to be toxic, especially propargyl alcohol based materials, which have been found to be very effective corrosion inhibitors. In addition to their toxic nature, these corrosion inhibitors are typically supplied as solutions in volatile organic solvents, which is unfavorable because of increased flammability.
Thus, there is a continuing need for improved and more environmentally benign methods and compositions for inhibiting acid corrosion in oil and gas operations.